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Two of our most successful theories, quantum mechanics and general relativity, are at odds with each other in a number of areas. They make conflicting predictions—and, for some time, the quest has been on to find a deeper theory, one that resolves the conflicts and provides a better view of reality. Such a theory would describe how gravity works at a quantum level, and as such it would be known as a theory of quantum gravity.

Theories of quantum gravity have been proposed, including string theory and loop quantum gravity. But these all suffer from a common problem—it’s currently nigh-impossible to test them. The effects of quantum gravity are only expected to appear at the Planck scale, which is so small that all our current theories break down there. And worse, this scale is far too small for researchers to come anywhere near probing it directly with current technology.

The upgraded Large Hadron Collider, which comes back online this year, will reach energies of 13 tera-electronvolts (TeV), nearly doubling its pre-upgrade performance. But if you were hoping it might be able to experimentally probe quantum gravity effects, don’t hold your breath—the expected energy needed is a staggering ten quadrillion (or 10^16) TeV.

But that doesn’t mean there’s no way to learn about the Planck scale world. A new study has tested predictions made by one quantum gravitational model—and, rather than a particle collider, the study made use of astronomy. The model predicts that, at the Planck scale, spacetime gets a bit "fuzzy," or "grainy"—and that this graininess has a measurable effect on the way light propagates.

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